自制的电火花穿孔机.doc

自制的电火花穿孔机
转贴的，我也回答不了具体总体。感谢Zhang56网友提供的电路图。
电火花打小孔工具
摆轮是手表最重要部件,其上下两个轴尖因不停来回转动,在润滑不良情况下,很易磨损,一些老旧表特别是无防震功能的老怀表更是主要损坏件之一,
修复方法主要有:1;更换整个摆轮~有原厂摆轮最好,但要注意其惯性距要一样,不然在调整走时快慢会有麻烦,最好是连游丝(整个震荡系统)一同更换~2;锡焊摆轴尖,早年有配件厂专生产一种轴尖,状如铆钉,先将旧轴适当磨短,然后将轴尖大头与摆轴锡焊接,但焊后很难达到同轴度要求,摆轮容易变色不是好办法~3;碰焊法;该法除要求焊接规范(压力,电流,时间)参数适当外,还有一大缺点,就是摆轴材质为炭素工具钢(相当于国内牌号T10A)由於含炭高,焊核因急剧冷却导致晶粒粗大,内应力增加,硬和碎都给后期修磨轴尖带来困难,该法在工业中只适用於低炭钢和镍合金如不锈纲等材质~4;只更换摆轴,此法更多缺点,由於摆轴除与摆轮配合,还要与游丝,下摆碟配合,在冲下旧摆轴和铆合新摆轴时,极易将摆轮弄变形,给后续调较带来更多问题,如果不是原厂配件,则更不宜采用~5;裁轴尖(广东人叫种车芯)方法是在已断轴尖根部打钻一小孔,压打入小钢丝,有时孔深不够还要焊锡以求牢固,优点是影响部位小,原断处下部凸台可作参考点,手艺好的师傅修后一般难以看出差别,缺点是需对摆轴退火,温度不足难钻孔,温度过高镀金摆轮将变色,钻头难磨,如果折断钻头则麻烦大了!
                                          早年搞了个电火花打孔工具,上图与朋友交流

电源箱.jpg (36.55 KB)
2009-6-23 13:59

由于要打之孔很小,又是盲孔,不能用晶体管电路,只能用原始的RC电路,变压器功率为10W,输出电压40VDC,50VDC两挡,电容为金属化纸介电容,分0.01nF.0.22nF.0.47nF按要求组合

整机图.jpg (44.04 KB)
2009-6-23 13:59

工具1基座为后置导柱.周界为80x80模架,稳定性高可保证电极与摆轮工作时的垂直度和平行度要求
1;为电极头,用DQK电磁先导伐改装,线圈不变由220VAC供电,下部静铁芯长度比线圈长度一半再少1.5mm,中间有孔,压装于线圈导磁套内,上部动铁芯长度一样,但外径少1.5mm,端部装轴承,由0.15mm3J1恒弹性十字簧片固定于线圈外壳,下部也有轴承,同样由十字簧片固定干外壳,转轴由两轴承支承,下部为夹头,夹持紫铜电极,上端有小皮带轮,也是导电入口,再由220VAC/500转同步电机带动,整个电极头垂直装于上模扳,并与之绝缘,工作时电极边旋转边上下震动~
2;为旋转平台,内有轴承,外部装有煤油承液盘,摆轮平放干平台上,由一金属环通过三个簧片以重力轻压摆轮,使其导电,整个平台垂直装于下模板上,并与上电极同轴~
3;为电极修正器,装于下模扳,可作水平摆动和固定,旋转手轮可使电极座3前后移动~
4;为修正电极,实为一废手锯片,电蚀不平时可折下重磨~
5;为摆轮调正对中器,装于上模扳并与之绝缘,可水平摆动和固定,旋动手轮带动一刀口片,推动摆轮轴颈以调节同轴度~
6;为电容插座,实为IC测试座,不同电容量组合均装夹干此,此种布置不同于常规,如将电器元件均装于电箱内通过电线引出,则因电容量少,电压低而放电回路长,电阻大,放电电流下降不陡,火花效率就差,所以一定要将电容尽量靠近电极,减少回路电阻很关键,否则必失败~
7;为上模扳升降旋纽,旋纽下部有刻度,分为100格,每格0.01mm~
电路图：

使用方法
先将摆轮轴尖根部园弧处端面稍磨平,放置于平台上,由重力压块将摆轮轻压于平台,注意要导电良好~将紫铜电极装夹于电极头,尽量调少旋转偏摆,电箱右上角选择旋纽置于(修极)位,电容量选0.47nF,电压选高,左下边开关打向上,将电极修正器置于适当位置并固定,打上电源开关,此时电极又旋又震,转动各旋纽,用反烤法烧蚀电极,当直径接近要求时,改用精规范,以提高电极表面不平度,可降低打孔时电极损耗,见图三

电极修正后关电源,将电极升高,不使影响调中工作,移开电极修正器,将摆轮调中器5调到适当位并固定之,电箝右上角旋纽置于(调中)位,电压开关打向低端,旁边开关置於中间位置,调节旋纽7和摆轮调中器5上白色手轮,使刀口接近已断摆轴下凸台,电箱内通过分压器取得的2VDC在串入蜂鸣器后加于刀口与轴颈之间,一边慢漫转动平台2,通过听声音确定摆轴对中与否,(见下图)

对中后关电源,移开调中器,电箱右上角旋纽置於(打孔)位置,电压开关扳向下方(低)此时电压为40VDC,电容取0.022-0.22nF,频率取高点,规范取精,左下边第三个开关扳向下方(铭牌有误,应为震动)此时打孔电极只震动不旋转,调节旋纽7使电极接近摆轴,开始打孔,可通过电压表指示协助进级,无火花时指示最高,当电压低于25VDC时应停止进级,到指针上升后再进级~(图五)

在修电极和打孔时应用毛笔粘媒油湿润火花处,打孔直径大可用粗规范反之则取精规范,孔深可由旋纽7之刻度读取,由
于电极也损耗,实际深度约为刻度值0.6,一般孔深为孔径2.5-3倍即可~

   由于有可重置的规范,减少个人手艺因素,免去磨钻头,断钻头的麻烦,加上无需退火,摆轮不会变形变色,巳用十数次,不
失为较好的修复方法~一点个人心得,算是抛砖引玉~

RC电路图.JPG (36.33 KB)
2009-11-1 16:22
修电极时先用粗规准,40V,0.22-0.47微法,精修电极时用30V,0.01-0.047微法,打孔时只用精规准,孔径大电容取大,反之取小.电容器安装尽量靠近电极和工件处,以减少放电回路的电阻!
A Mini-EDM System
Overview
I built a small EDM system, primarily for burning out broken-off taps in aluminum parts. But, now that I see how easily it works, I can see many other things that it could be used for. I built this whole system over a weekend, entirely out of parts I had laying around. (I do have a lot of pieces, both electronic and mechanical.)
Electrode

The electrode I made up consisted of a piece of .060 brazing wire soldered into the socket of an 8-32 socket-head cap screw. I threaded this into a nylon spacer that I happened to have, that already had an 8-32 threaded hole in it. I put the spacer into the drill chuck on my mill. The nylon spacer is the insulator that prevents the electrode from grounding out to the chuck, and the rest of the milling machine. I connected the power supply to the electrode by way of a soft stranded wire, so that the wire wouldn't deflect the brazing rod. The end of the wire was stripped back about one inch, and the wire strands were loosely wrapped around the brazing rod. This made a remarkably good electrical contact, while allowing the brazing rod to turn freely. I could put just a slight bend in the rod so that it would make a very slight (ie. .010") orbit if the spindle were rotated. This seemed to get the best metal removal and depth progress before the hole got filled with removed metal and shorted out.

A view of the EDM electrode assembly in a Jacob's chuck.
Power Supply
The power supply I threw together was quite simple. A variac (variable autotransformer) is used to adjust output voltage. A 200 Watt variac (1-2 Amps at 110 V) is quite adequate. A step-down transformer, which provides isolation, is the next component. The one I used was center-tapped, allowing the use of 2 rectifiers. If your choice of transformer does not have the center tap, or the voltage is too low when using it, you could use a bridge rectifier on the two outer connections of the secondary to get higher voltage. A filter capacitor provides smoothing of the DC voltage produced. A resistor allows the electrode to short to the work without blowing fuses, and also moderates the flow of current from the raw DC supply to the EDM capacitor and electrode. Choose a resistance that will cause a short circuit current at least twice the desired EDM current at the selected voltage. Then, make sure the wattage is sufficient to prevent the resistor burning up during a few seconds of short circuit. With the DC supply set to 30 Volts, a short would draw approximately 1 Amp, and since P=I^^2 * R, that is about 30 W, using a 30 Ohm Resistor. The ammeter shows current into the EDM capacitor. The EDM capacitor delivers short bursts of very high current whenever the insulating film of the EDM fluid gets very thin between the electrode and workpiece.

EDM Fluid
Not having distilled water around, I tried tapwater. It was boiled away very quickly by electrolysis, and didn't do much good even when it was there (perhaps all that bubbling got in the way of the EDM process). I then tried the nearest thing at hand, which was "Alum-Tap", a light, clear tapping fluid for aluminum. It must be pretty close to EDM fluid, because it worked so well! It lasted a long time before being spattered away by the gases generated by the EDM action. Most of the time, I only had to add a few drops before the hole became filled with removed metal.
Operation
The way I set this up was pretty much by trial and error. But, here are my settings: I set the power supply for 30 Volts. This seemed to give a very strong discharge action without producing too much gas or heat. I lowered the electrode with my NC control's jog buttons until I got electrode contact (indicated by about 1 Amp current suddenly appearing on the ammeter). I then raised the electrode with a very slow jog until the current dropped to zero. I then entered a manual command to advance the electrode at a rate of about .010" / minute, and after a few seconds, the ammeter would show a current of 1/4 to 1/2 amp. I would modulate the feedrate with the feedrate override controls, attempting to keep the current within these limits. By bending the electrode just a tiny bit, and running the mill's spindle at the slowest speed (80 RPM), I could get any diameter hole I wanted. I set it to just keep a tiny bit of the flank of the tap, but to burn out the entire web (central portion) of the tap. This allowed me to pick the remaining part of the tap's cutting edge out of the aluminum easily with a fine needle when the EDM electrode had cut all the way through. Progress all the way through was evident when the tool was still advancing with no EDM current.
Since I didn't have a means of providing a flow of EDM fluid through such a small electrode, I had to pull the electrode up every .025" or so, wipe out the contaminated fluid with a paper towel, and then drip a few drops of the Alum-Tap into the hole.